Semiconductor device and method of making the same

ABSTRACT

A semiconductor device and a method of making a semiconductor device are provided, wherein the device includes a die-pad, a semiconductor chip and a sealing resin. The die-pad has a first surface and a second surface opposite to the first surface. The second surface includes an exposed portion and a retreated portion around the exposed portion. The semiconductor chip is mounted on the first surface of the die-pad. The sealing resin covers the die-pad and the semiconductor chip, exposes the exposed portion, and is held in contact with the retreated portion.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention:

[0002] The present invention relates to a semiconductor device of theQuad Flat Non-leaded (QFN) package type, and a method of making thesame.

[0003] 2. Description of the Related Art:

[0004]FIG. 6 is a plan view showing a prior art semiconductor device S3of the Quad Flat Non-leaded (QFN) package type. FIG. 7 is a sectionalview taken along lines VII-VII of FIG. 6. The semiconductor device S3includes a semiconductor chip 31, a die-pad 32 on which thesemiconductor chip 31 is mounted, a plurality of leads 33, and a sealingresin 34 which is illustrated as transparent in FIG. 6. Thesemiconductor chip 31 is electrically connected to the die-pad 32 via afirst wire 41 for grounding. Each of the leads 33 is electricallyconnected to the semiconductor chip 31 via a second wire 42. The sealingresin 34 seals the semiconductor chip 31, the first wire 41 and thesecond wires 42 while exposing the lower surface 32 b of the die-pad 32and part of each lead 33.

[0005] In the semiconductor device S3, the lower surface 32 b of thedie-pad 32 is exposed to the outside. Therefore, as indicated by thearrow A in FIG. 8, water is likely to enter through the boundary betweenthe die-pad 32 and the sealing resin 34 and may reach the upper surface32 a of the die-pad 32. In the reflowing process for mounting thesemiconductor device S3 onto a mother board (not shown), when thedie-pad 32 is heated while containing water on the upper surface 32 a,the sealing resin 34 is removed from the die-pad 32 to shrink in thearrow B direction. As a result, the sealing resin 34 exerts a stress tothe first wire 41, which may lead to the breakage of the first wire 41.

SUMMARY OF THE INVENTION

[0006] It is therefore an object of the present invention to provide asemiconductor device having a high reliability by preventing the removalof a sealing resin due to water infiltration.

[0007] According to a first aspect of the present invention, asemiconductor device is provided. The semiconductor device comprises; adie-pad having a first surface and a second surface opposite to thefirst surface, the second surface including an exposed portion and aretreated portion around the exposed portion; a semiconductor chipmounted on the first surface of the die-pad; a sealing resin forcovering the die-pad and the semiconductor chip, wherein the resin isheld in contact with the retreated portion while exposing the exposedportion.

[0008] Preferably, the retreated portion comprises a retreated surfaceand a side surface which adjoins the exposed portion, and the retreatedsurface forms an acute angle together with the retreated surface.

[0009] Preferably, the die-pad includes a slit opening at the retreatedsurface of the second surface and at the first surface.

[0010] Preferably, the die-pad includes a plurality of slits opening atthe retreated surface of the second surface and at the first surface,and the plurality of slits are arranged to surround the semiconductorchip.

[0011] Preferably, the semiconductor chip is electrically connected tothe die-pad via a first wire, and the first wire is connected to thefirst surface of the die-pad at a portion between a peripheral edge ofthe die-pad and the slit.

[0012] Preferably, the semiconductor device further comprises a terminalelectrically connected to the semiconductor chip via a second wire. Theterminal is retained by the sealing resin so as to expose a partthereof.

[0013] According to a second aspect of the present invention, anothersemiconductor device is provided. The semiconductor device comprises; asemiconductor chip; a die-pad which has an upper surface on which thesemiconductor chip is mounted and a lower surface opposite to the firstsurface, the die-pad being electrically connected to the semiconductorchip via a first wire; and a plurality of leads electrically connectedto the semiconductor chip via second wires, the semiconductor chip beingsealed with a sealing resin with the lower surface of the die-padexposed. The die-pad includes a thin-walled portion formed by removingthe lower surface along a peripheral edge of the die-pad and alsoincludes at least one slit penetrating through the thin-walled portion.

[0014] Preferably, the sealing resin extends under the thin-walledportion so as not to expose an opening of the slit.

[0015] Preferably, the slit is provided along a side surface of thesemiconductor chip so as to surround the semiconductor chip.

[0016] Preferably, the first wire is connected at one end thereof to thesemiconductor chip and connected at the other end thereof to the die-padat a portion between a peripheral edge and the slit.

[0017] According to a third aspect of the present invention, asemiconductor device making method comprises the steps of; punching aconductive frame to form a die-pad having an upper surface and a lowersurface opposite to the upper surface, and to form a slit penetratingthrough the die-pad adjacent the peripheral edge of the die-pad;performing etching with respect to the lower surface along theperipheral edge of the die-pad to form a thin-walled portion in thedie-pad so that the slit opens at the thin-walled portion; mounting asemiconductor chip on the upper surface of the die-pad; bonding thesemiconductor chip and the die-pad via a wire; and sealing thesemiconductor chip with a sealing resin so that the lower surface of thedie-pad is exposed.

[0018] Other features and advantages of the present invention willbecome clearer from the detailed description given below with referenceto the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a plan view showing a semiconductor device according toa first embodiment of the present invention;

[0020]FIG. 2 is a sectional view taken along lines II-II of FIG. 1;

[0021]FIG. 3 is a sectional view showing a semiconductor deviceaccording to a second embodiment of the present invention;

[0022]FIG. 4 illustrates a method of making a semiconductor deviceaccording to the present invention;

[0023]FIG. 5 illustrates a method of making a semiconductor deviceaccording to the present invention;

[0024]FIG. 6 is a plan view showing a prior art semiconductor device;

[0025]FIG. 7 is a sectional view taken along lines VII-VII of FIG. 6;and

[0026]FIG. 8 illustrates how the removal of the sealing resin occurs.

BEST MODE FOR CARRYING OUT THE INVENTION

[0027] Preferred embodiments of the present invention will be describedbelow in detail with reference to FIGS. 1-5.

[0028]FIG. 1 is a plan view showing a semiconductor device S1 accordingto a first embodiment of the present invention. FIG. 2 is a sectionalview taken along lines II-II of FIG. 1. The semiconductor device S1includes a semiconductor chip 1 having an upper surface 1 a and sidesurfaces 1 b, a die-pad 2 having an upper surface 2 a and a lowersurface 2 b, a plurality of leads 3 for connection to externalterminals, a sealing resin 4 which is illustrated as transparent in FIG.1, a first wire 11 for grounding, and a plurality of second wires 12.

[0029] The semiconductor chip 1, which maybe an LSI chip or another kindof IC chip for example, is a silicon chip having one surface on whichdesired integrated electronic circuit is formed. The upper surface 1 aof the semiconductor chip 1 is provided with a plurality of electrodepads (not shown). For obtaining good conductivity, the electrode padsmay be formed by gold-plating electrodes of aluminum formed on the uppersurface 1 a of the semiconductor chip 1.

[0030] The first wire 11, which may be formed of gold for example, isbonded, at one end thereof, to the electrode pad for ground connectionof the semiconductor chip 1. The other end of the first wire 11 isconnected to the upper surface 2 a of the die-pad 2. Generally, when thesemiconductor device S1 is surface-mounted onto a mother board (notshown), the lower surface 2 b of the die-pad 2 is connected to a groundpattern formed on the mother board. In this way, the grounding of thesemiconductor chip 1 is realized via the first wire 11.

[0031] Each of the second wires 12, which may be formed of gold forexample, is bonded, at one end thereof, to a respective one of otherelectrode pads on the semiconductor chip 1. The other end of the secondwire 12 is connected to the upper surface 3 a of a corresponding one ofthe leads 3 arranged around the semiconductor chip 1.

[0032] The die-pad 2 is a thin metal plate of a predetermined thicknessformed of copper for example and larger than the semiconductor chip 1.The semiconductor chip 1 is bonded, via an adhesive, to a centralportion on the upper surface 2 a of the die-pad 2. The die-pad 2includes a thin-walled portion 5 formed by cutting away peripheralportions of the lower surface 2 b.

[0033] The thin-walled portion 5 has a thickness which is about one halfof that of other portions of the die-pad 2. On the lower surface side 2b of the die-pad 2, the thin-walled portion 5 is defined by a retreatedsurface 6 a and a side surface 6 b. In this embodiment, the side surface6 b extends generally perpendicularly to the retreated surface 6 a. Thethin-walled portion 5 is formed with a plurality of thickness wisepenetrating slits 9 arranged to surround the semiconductor chip 1. Asclearly shown in FIG. 1, each of the slits 9 extends along a respectiveside surface 1 b of the semiconductor chip 1. One end of the first wire11 is connected to the electrode pad provided on the upper surface 1 aof the semiconductor chip 1 as described before, whereas the other endof the first wire is connected onto the die-pad 2 at a portion betweenthe slit 9 and a peripheral edge of the die-pad 2. Thus, the first wire11 bridges the slit 9.

[0034] Similarly to the die-pad 2, the leads 3 are formed from a thinmetal plate of copper for example. The leads 3 are spaced from eachother along the side surfaces 1 b of the semiconductor chip 1.

[0035] The sealing resin 4 may be formed of a thermosetting resin suchas an epoxy resin. As clearly shown in FIG. 2, the sealing resin 4 sealsor covers the semiconductor chip 1, the first wire 11, the second wires12, the upper surface of the die-pad 2 and the leads 3, while exposingpart of the lower surface 2 b of the die-pad 2, the lower surfaces 3 band the side surfaces 3 c of the leads 3 to the outside. Since thesealing resin 4 encloses the thin-walled portion 5 of the die-pad 2, theopenings 9 a of the slits 9 formed in the thin-walled portion 5 are notexposed to the outside.

[0036] To surface-mount the semiconductor device S1 onto a substrate(not shown), solder paste is applied to the wiring pattern formed on thesubstrate. Then, the device S1 is placed on the substrate so that thelower surface 2 b of the die-pad 2 and the lower surfaces 3 b of therespective leads 3 come into contact with the solder-applied wiringpattern. Precisely, the lower surface 2 b of the die-pad 2 is broughtinto contact with the grounding portion of the wiring pattern. After thedevice S1 is properly positioned on the substrate, the applied solderpaste is heated up so as to perform reflow soldering. As a result, thedevice S1 is electrically connected to the substrate via the die-pad 2and the leads 3.

[0037] According to the semiconductor device S1 having the abovestructure, water infiltration to the upper surface 2 a of the die-pad 2can be prevented or lessened. In the semiconductor device S1, since thedie-pad 2 and the sealing resin 4 have a boundary exposed to theoutside, water may enter through the gap between the side surface 6 band the sealing resin 4. However, owing to the retreated surface 6 aextending perpendicularly to the side surface 6 b, the progress of watercan be terminated. Thus, water is unable to reach or less likely toreach the upper surface 2 a of the die-pad 2, whereby the removal of thesealing resin 4 in the reflowing process is reliably prevented.Consequently, it is possible to provide a reliable semiconductor devicein which the breakage of the first wire 11 due to the removal of thesealing resin 4 does not occur.

[0038] In the semiconductor device S1, the sealing resin 4 surrounds thethin-walled portion 5 and fills the slits 9 provided at the thin-walledportion 5. This provides an ‘anchoring effect’ contributing to securebonding between the die-pad 2 and the sealing resin 4. Thus, the die-pad2 and the sealing resin 4 are irremovably attached to each other. Sincethe sealing resin 4, extending around and under the thin-walled portion5, fills the openings 9 a of the slits 9, water filtration through theslits 9 can be completely prevented or significantly lessened.

[0039] Further, in the semiconductor device S1, part of the sealingresin 4 extends into the plurality of slits 9 formed in the die-pad 2for engagement therewith. Therefore, even if water reaches the uppersurface 2 a of the die-pad 2, thereby causing the sealing resin 4 tocome off the surface at a location adjacent to the semiconductor chip 1,the slits 9 around the semiconductor chip 1 prevent the resin removalfrom propagating toward the peripheral edges of the die-pad 2 beyond theslits. Since the first wire 11 is connected at one end to thesemiconductor chip 1 and at the other end to a portion of the die-pad 2that is located between the slit 9 and the peripheral edge of thedie-pad 2, the removal of the sealing resin does not affect the firstwire 11. Therefore, the bonding condition of the first wire 11 to thedie-pad 2 is kept good.

[0040] For preventing the removal of the resin seal 4, each of the slits9 may be formed in the die-pad 2 at a portion inward from thethin-walled portion 5. In such a case, however, the opening 9 a of theslit 9 is exposed to the outside, which increases the possibility thatwater advances along the inner surfaces of the slit 9 to reach the uppersurface 2 a of the die-pad 2. Therefore, in view of the prevention ofwater infiltration, it is preferable that the slit 9 is so formed as topenetrate through the thin-walled portion 5. Instead of the slit 9, theupper surface of the die-pad 2 may be formed with a recess forengagement with the sealing resin 4. In this case, since the recess isnot open at the lower surface 2 b of the die-pad 2, water filtration canbe prevented even when the recess is provided inward from thethin-walled portion 5 in the die-pad 2.

[0041]FIG. 3 is a sectional view showing a semiconductor device S2according to a second embodiment of the present invention. Thesemiconductor device S2 differs from the semiconductor device S1 inconfiguration of side surface 6 b. In the second embodiment, the sidesurface 6 b extends toward the center of the semiconductor chip 1 as itapproaches the retreated surface 6 a. That is, the side surface 6 btogether with the retreated surface 6 a forms an acute angle. Otherportions are configured in a way similar to those of the above-describedsemiconductor device S1.

[0042] In the semiconductor device S2, the sealing resin 4 comes intomore secure contact with the die-pad 2, so that the die-pad 2 and thesealing resin 4 are held together more stably. However, theconfiguration of the side surface 6 b is not limited to those describedabove, and another configuration may be employed as long as it ensuresclose contact between the die-pad 2 and the sealing resin 4.

[0043] Referring now to FIGS. 4 and 5, a semiconductor devicefabrication method of the present invention will be described below.First, an elongated conductive frame 15 is prepared. Then, as shown inFIG. 4, punching and pressing is performed with respect to theconductive frame 15. Specifically, the punching and pressing withrespect to the conductive frame 15 is performed to provide two supportbars 17 each formed with a plurality of perforations 16 arranged at apredetermined pitch, and to provide a plurality of die-pads 2 betweenthe support bars at a predetermined pitch longitudinally of theconductive frame 15. At this time, with respect to each of the die-pads2, connection leads 18 for supporting the die-pad 2 are formed at therespective corners of the pad. Further, a plurality of slits 9 areformed adjacent to the peripheral edges of the die-pad 2. A plurality ofleads 3 are formed around the die-pad 2.

[0044] Subsequently, with respect to each of the die-pads 2, portions ofthe lower surface 2 b adjacent the peripheral edges thereof are removedby etching so that a thin-walled portion 5 is provided. The portionsetched include portions in which the slits 9 are formed. At this time,the portions adjacent the peripheral edges of the die-pad 2 may beetched by e.g. wet etching to a thickness which is about one half ofthat of other portions. Alternatively, the thin-walled portion 5 may beformed by a punching process together with other portions if these otherportions have a sufficiently large thickness. The configuration of theframe 15 shown in FIG. 4 may be provided by an etching process.

[0045] Next, a semiconductor chip 1 is mounted by die-bonding to thecenter of the upper surface 2 a of each die-pad 2. Then, a first wire 11is bonded to the electrode pad for grounding of the semiconductor chip 1and the upper surface 2 a of the die-pad 2. With respect to the die-pad2, the first wire 11 is bonded at a portion between the slit 9 and theperipheral edge of the die-pad 2. Then, a second wire 12 is bonded toconnect each of other electrode pads of the semiconductor chip 1 to acorresponding one of the leads 3.

[0046] Then, as shown in FIG. 5, the frame 15 is interposed between anupper mold member 21 and a lower mold member 22. At this time, the lowersurface 2 b of each die-pad 2 (except for the thin-walled portion 5) andthe lower surfaces 3 b of the respective leads 3 are brought intocontact with the lower mold member 22. Then, a packaging resin such asan epoxy resin in a molten state is supplied to fill the cavity definedby the upper mold member 21 and the lower mold member 22. This resin isthen solidified. At this time, no clearance is formed between the lowersurfaces 3 b of the leads 3 and the lower mold member 22, and betweenthe lower surface 2 b of the die-pad 2 (except for the thin-walledportion 5) and the lower mold member 22. Therefore, the lower surfaces 3b and the lower surface 2 b (except for the thin-walled portion 5) arenot covered with the resin. After the resin is solidified, theresin-packaged semiconductor device S1 is removed from the upper and thelower mold members 21, 22. Then, unnecessary portions of the leads 3 arecut away. As a result, the resin-packaged semiconductor device S1 isobtained.

[0047] The semiconductor device S2 can also be formed by theabove-described fabrication method. In forming the thin-walled portion 5of the semiconductor device S2, the side surface 6 b, which forms anacute angle together with the retreated surface 6 a, may be formed byperforming over-etching.

[0048] The scope of the present invention is not limited to theabove-described embodiments. For example, the structure of thesemiconductor chip 1, and the material, configuration, size of thedie-pad 2 are not limited to the above-described embodiments.

1. A semiconductor device comprising: a die-pad including a firstsurface and a second surface opposite to the first surface, the secondsurface including an exposed portion and a retreated portion around theexposed portion; a semiconductor chip mounted on the first surface ofthe die-pad; and a sealing resin covering the die-pad and thesemiconductor chip, the resin allowing the exposed portion to be exposedand being held in contact with the retreated portion.
 2. Thesemiconductor device according to claim 1, wherein the retreated portionis defined by a retreated surface and a side surface which adjoins theexposed portion and forms an acute angle together with the retreatedsurface.
 3. The semiconductor device according to claim 1, wherein thedie-pad is formed with a slit that is opened in the retreated surface ofthe second surface and in the first surface.
 4. The semiconductor deviceaccording to claim 1, wherein the die-pad is formed with a plurality ofslits that are opened in the retreated surface of the second surface andin the first surface, the plurality of slits being arranged to surroundthe semiconductor chip.
 5. The semiconductor device according to claim3, wherein the semiconductor chip is electrically connected to thedie-pad via a first wire, the first wire being connected to the firstsurface of the die-pad at a portion between a peripheral edge of thedie-pad and the slit.
 6. The semiconductor device according to claim 1,further comprising a terminal electrically connected to thesemiconductor chip via a second wire, the terminal being retained by thesealing resin so as to be partially exposed.
 7. A semiconductor devicecomprising: a semiconductor chip; a die-pad including an upper surfaceon which the semiconductor chip is mounted and a lower surface oppositeto the first surface, the die-pad being electrically connected to thesemiconductor chip via a first wire; a plurality of leads electricallyconnected to the semiconductor chip via second wires; and a sealingresin enclosing the semiconductor chip in a manner such that the lowersurface of the die-pad is exposed; wherein the die-pad includes athin-walled portion formed by removing a part of the lower surface alonga peripheral edge of the die-pad, the die-pad being formed with at leastone slit extending through the thin-walled portion.
 8. The semiconductordevice according to claim 7, wherein the sealing resin extends under thethin-walled portion so as not to expose an opening of the slit.
 9. Thesemiconductor device according to claim 8, wherein the slit extendsalong a side surface of the semiconductor chip around the semiconductorchip.
 10. The semiconductor device according to claim 8, wherein thefirst wire is connected at one end thereof to the semiconductor chip andconnected at another end thereof to the die-pad at a portion between aperipheral edge of the die-pad and the slit.
 11. A method of making asemiconductor device comprising the steps of: punching a conductiveframe to form a die-pad with a slit, the die-pad including an uppersurface and a lower surface opposite to the upper surface, the slitextending through the die-pad at a location adjacent to a peripheraledge of the die-pad; etching the lower surface along the peripheral edgeof the die-pad so as to form a thin-walled portion in the die-pad in amanner such that the slit is opened at the thin-walled portion; mountinga semiconductor chip on the upper surface of the die-pad; bonding a wireto the semiconductor chip and to the die-pad; and sealing thesemiconductor chip with a sealing resin in a manner such that the lowersurface of the die-pad is exposed.